A Russian strike destroyed a crowded children’s hospital in the center of Kyiv, Ukraine, on Monday, part of a large-scale aerial bombardment that killed at least 20 people in cities across the country.

At least 50 people were wounded in the barrage, according to Ihor Klymenko, the head of the ministry of internal affairs. Officials cautioned that the toll would likely rise.

In Kyiv, local authorities said at least nine people had been killed and another 23 wounded. It was not clear how many of the casualties were at the Okhmatdyt Children’s Hospital or at other locations in the city, where fires were reported after debris from missiles that had been shot out of the sky crashed into residential neighbourhoods.

President Volodymyr Zelensky of Ukraine said people were still trapped under the rubble at the hospital, and that the exact number of casualties was not yet known.

Shortly after the strike, a woman carried a small child covered in dust and blood near the entrance of the children’s hospital, Ukraine’s largest.

A desperate search and rescue operation was underway there on Monday afternoon, with the mayor of Kyiv, Vitali Klitschko, saying that more than 100 rescuers were on the scene. Outside the hospital, civilians formed a human chain to help clear the rubble brick by brick. Doctors and others inside the hospital — which treats 20,000 children annually — shared images of blood stained hallways, collapsed ceilings and destroyed operating rooms.

Ukrainian health minister Viktor Lyashko said that intensive care units, operating rooms and the oncology department had all sustained damage. The first task for the hospital staff, he said, was to transport patients to other facilities. Zelensky condemned the attack on the hospital, which he said “has been saving and restoring the health of thousands of children”.

“Russia cannot claim ignorance of where its missiles are flying and must be held fully accountable for all its crimes,” he said in a statement. “It is very important that the world does not remain silent about this now, and that everyone sees what Russia is and what it is doing.”

He said Russia directed at least 40 long-range missiles at targets across Ukraine, and there were reports of damage in Dnipro, Kryvyi Rih, Slovyansk and Kramatorsk.

The attack came the day before Nato leaders were scheduled to gather in Washington for an annual summit, where they were expected to announce plans to bolster Ukraine’s air-defence capabilities.

Vsevolod Dorofieiev, the senior instructor of a volunteer medical unit, said some people had died but he did not say how many or whether they were children or adults.

The daylight attacks included Kinzhal hypersonic missiles, one of the most advanced Russian weapons, the Ukrainian air force said.

The Kinzhal flies at 10 times the speed of sound, making it hard to intercept.